Method and apparatus for correlated ophthalmic measurements

ABSTRACT

A method and system providing multiple ophthalmic and retinal blood measurements is outlined. By extracting multiple digitized wavelength images and quantitative data within a relatively short time period the method allows for compensation of a patients eye or head movement, generation of ophthalmic clinical records, and determination of data relating to blood measurements, such as oxygen saturation and hemoglobin, in addition to ocular and other disease determinations. The method provides for multiple analysis and measurements within a single sitting of the patient, with a single simple instrument and without adaptations to the instrument during a patients eye examination. Beneficially the approach allows for low cost, compact, and even portable implementations offering such analysis and determination outside the current ophthalmic centers providing eased access and earlier diagnosis opportunities.

This application claims the benefit of U.S. Provisional Application No. 60/879,793, filed on Jan. 11, 2007, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to ophthalmic analysis and more particularly to using time and wavelength based imaging to provide multiple analyses with reduced constraints on equipment and patient.

BACKGROUND OF THE INVENTION

Historically, visits to an ophthalmic specialist or eye center were based upon obtaining a measure of the patients reading quality as a function of distance, color and text dimension. Then based upon these the patient was assessed using a wide variety of graduated lenses to provide a simple three value characterization for each eye of the appropriate lens to correct for common visual defects such as shortsightedness, long-sightedness, and peripheral focus.

In recent years an important trend in such visitations to an ophthalmic center has been the addition of a limited number of diagnosis for the early onset of conditions such as diabetes. Generally, each such diagnostic addition is performed by provisioning of a further evaluation station within the ophthalmic center such that the patient moved along with the ophthalmetrist to each evaluation station in turn. At each station the patient is required to hold their head in a steady position within a restraint, and to keep their eye open for extended periods whilst the ophthalmetrist assessed their health or visual acuity.

Such a requirement for multiple evaluation stations places constraints on the provisioning of such ophthalmic tests for patients to locations with significant floor area, requires the centers providing the services to invest heavily in capital equipment, and provides a psychological barrier to patients in having frequent check-ups and assessments. More significantly, a single file must pass from system to system for storing of results therein or data of one patient ends up in another patients file. Management of patient data is important if screening tests are to be meaningful.

One approach to managing patient data is to test a single patient at a time. In such a situation, all systems are unused except one. This is an inefficient use of resources. Unfortunately, for a very efficient use of resources, file management becomes extremely difficult with several tests performed on different patients in parallel.

It would therefore be beneficial to provide an ophthalmic instrument that allowed a plurality of ophthalmic tests to be performed upon a patient in a single sitting with a single sequence of measurements that did not require reconfiguration of the ophthalmic instrument during the sitting. Advantageously, such a single sequence of measurements provides for a correlation of results from these different measurements and allows for the incorporation of weightings or adjustments into the analysis of one characteristic based upon measurements and analysis of another characteristic. This being possible as these measurements are now associated with defined time differences, the time between measurements being reduced with such a single setting and single sequence of ophthalmic measurements, and the conditions of the measurements being more consistent than moving a patient between multiple test stations over an extended period of time.

Advantageously, where there correlation between measurements is of increased interest then the sequence of tests within the ophthalmic instrument can be changed simply, such as with software reconfiguration of the testing sequence. Further, the ability to provide consistent time differences between different measurements allows improved correlation of the measurements not only within a single sitting but across the multiple sittings of a patient over time with their repeat visits. Additionally, the defined time stamps of the different measurements allows the subsequent analysis of the measurement data for an additional or new characteristic at a later date, a potential which today does not exist.

Additionally, automating multiple measurements within a single sitting provides opportunities to expand the provisioning of the tests based upon ophthalmic measurements, including but not limited to, blood flow, oxygen saturation, deployed outside ophthalmic centers into doctor's offices, dentists, and even wider providing enhanced diagnosis and early identification of diseases or conditions thereby lowering health care expenditures and potentially saving lives.

It is therefore an object of this invention to provide such a beneficial method of providing within a single sitting multiple ophthalmic measurements providing enhanced correlation of the measurements and analysis.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a system for performing ophthalmic measurements comprising an optical source, the optical source comprising at least a control port, the optical source for providing a source optical signal at least one of a plurality of predetermined wavelengths, the one of the plurality of predetermined wavelengths being established in dependence of a control wavelength signal provided to the control port. Also provided is a digital detector, the digital detector comprising at least an output port, the digital detector for receiving a detected optical signal, generating at least a digital representation of a detected optical signal, and providing the digital representation of a detected optical signal at the output port as a detected electrical signal. An optical coupling is provided for coupling the source optical signal to a patients eyeball, receiving at least a reflected signal to an eyeball of the patient, and providing the reflected optical signal to the digital detector, the reflected optical signal therefore forming at least a portion of the detected optical signal.

Also provided is a controller, the controller being electrically connected to at least the control port and output port, the controller for providing at least one of a plurality of control wavelength signals, receiving the detected electrical signal, and providing a processed electrical signal, the processed electrical signal being determined at least in dependence upon the detected electrical signal, the control wavelength signal, and a predetermined factor.

In accordance with another aspect of the invention there is provided a method of providing an ophthalmic instrument, comprising at least a multi-wavelength optical source, an optical wavelength filter, and a digital detector. The ophthalmic instrument for providing a digital output determined in dependence upon at least a state of the machine and the wavelength of the multi-wavelength optical source. There is also provided a rest, the rest for providing a predetermined relationship between a patients head engaged with at least the rest and the ophthalmic instrument; and thereby determining with a single placement of the patients head with respect to the ophthalmic instrument at least one of a plurality of measurements of the patient, the measurements determined in dependence upon at least one digital output.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which:

FIG. 1 illustrates a schematic of an exemplary ophthalmic system according to the invention.

FIG. 2 illustrates an exemplary visualization of the retinal reflections as exploited by an exemplary embodiment of the invention for providing an oxygen saturation measurement without calibration.

FIG. 3 illustrates an exemplary flow chart for providing an hemoximeter functionality within an exemplary embodiment of the invention for hemoglobin measurements.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1 shown is a schematic of an exemplary ophthalmic system 100 according to the invention. Shown within the ophthalmic system 100 are an optical source 130 capable of providing light at the wavelengths necessary for the tests to be performed with the images and data extracted using the ophthalmic system 100. Such a light source typically being a tungsten lamp for high efficiency, high optical illumination and broad wavelength provisioning.

The emission from the optical source 130 is collimated using first lens 125 and coupled to a wavelength filter element 120 that selects the wavelength for a measurement to be performed. As shown the wavelength filter element 120 and optical source 125 are electrically interconnected to a central controller 140 which provides for management of the wavelength filter element 120 and optical source 125 during the measurement procedures under control of software operating upon a microprocessor, not shown for clarity but optionally embedded within the central controller 140.

The output light of the wavelength filter element 120, being a wavelength slice of the emission from the optical source 130 is coupled via optical element 115 to the second lens 110 wherein it is coupled to the patients eyeball 150 via their corneal lens 105. Light reflected from the retina 160 of the patient's eyeball 150 is then coupled back through the corneal lens 105 and second lens 110 to the optical element 115. Optical element 115 provides the functionality of a beam splitter in that the reflected light impinging onto the optical element now exits from a port of the optical element that is not the same as the light initially coupling into the optical element 115 from the optical source 130. In this manner the reflected signal is isolated from the optical source 130. The reflected signal upon exiting the optical element 115 is coupled to the CCD array 155.

The CCD array 155 is electrically coupled to the central controller 140 allowing the image of the patient's retina 160 to be extracted. In this exemplary embodiment the extracted CCD image is provided either to a display 135 or a storage device 145. It would be evident to one skilled in the art that the CCD data may be handled in many different manners, including but not limited to being stored without processing, stored with processing, displayed with processing, processed in conjunction with an algorithm stored within the central controller, processed in conjunction with other wavelength images, have qualitative data extracted from the image, and have qualitative data extracted in dependence upon multiple extractions with varying optical source intensity. Further, the CCD image may be processed such that for all wavelengths extracts the images are aligned within a predetermined image template according to a physically extracted feature of an image. In this manner the ophthalmic system 100 allows for movement of the patients eyeball 150 during a sequence of multiple images either from motion of the patients eyeball 150 itself or the patients head, not shown for clarity.

An exemplary embodiment of the use of an ophthalmic system 100 as presented in respect of FIG. 1 is now described for an oxygen saturation measurement without calibration. The model describing the light reflection and absorption by the different layers in the human eye in this exemplary embodiment was adopted from the early model developed by van Norren & Tiemeijer (1986) and Delori & Pflibsen (1989). A similar model, which further includes the receptor layer ignored in earlier models, was presented by van de Kraats, Berendschot & van Norren (1996) and Faubert & Diaconu (2001) and may be optionally employed in this determination. In this model, as shown schematically in FIG. 2 the pigment epithelium 290 and the sclera 270 are the principal reflectance layers and the eye media 240, macular pigment 280, melanin 275, photoreceptor photo pigments 230, together with hemoglobin and oxygenated hemoglobin represent layers where light is absorbed.

According to FIG. 2, an incident light of intensity I0λ), we obtain a reflected light with two components: one from the pigment epithelium layer 290 and one from the sclera 270 A mathematical description is shown by the following equations (1) and (2)

IR1(λ)=I0(λ)*10^(−2(D1(λ)+D2(λ)+Dp(λ))) *R1(λ)*C(λ)  (1)

IR2(λ)=I0(λ)*10^(−2(D1(λ)+D2(λ)+Dp(λ)+D3(λ)+D4(λ)+D5(λ))) *R2(λ)*(1−R1(λ))² C(Ω)  (2)

Where I_(R1)(λ) represents the spectral flux reflected by the pigment epithelium 290 the I_(R2)(λ) represents the spectral flux reflected by the sclera 270. The constant C(Ω) represents that only a small fraction of the reflected light exiting through the solid angle of the fundus point and the pupil surface. For human eye dimensions and for a typical pupil of 4 mm in diameter, we can assume that C(λ) equals 10⁻².

The reflection coefficients of the epithelium and the sclera are represented by the R₁(λ) and R₂(λ) respectively. In the equation (2) the expression (1−R₁(λ))² determines that the reflected light from the sclera 270 supports two partial reflections from the epithelium layer 290. The different absorbing layers are represented in the formulas by the values Di(λ) for optical spectral density. For a homogeneous medium, the optical spectral density can be described by the following formula:

D(λ)=ε(λ)*d*c  (3)

where E(λ) represents the spectral extinction coefficient, d is the optical path length of the light in the absorbing layer, and c is the concentration of the absorbing molecules in the medium. In this exemplary embodiment the optical density of different layers in the eye has been assumed to be expressed by a function F(λ) that is constant across subjects, i.e. the normalized spectral density function is constant, multiplied by a subject dependent coefficient m:

D

=F(λ)*m  (4)

where m varies as a function of optical path length d and concentration c.

Hence, from Equations (1) and (2) we can express the reflected light from the fundus of the eye as:

IR(λ)=IR1(λ)+IR2(λ)  (5a)

and

IR(λ)=I0

*10^(−2(D1(λ)+D2(λ)+Dp(λ)) *[R1(λ)+10^(−2(D3(λ)+D4(λ)+D5(λ))) *R2

*(1−R1

)2]*C(Ω)  (5b)

Now using the expression: D(λ)=F

*m for the optical density we can rewrite the equation (5b) as:

$\begin{matrix} {{{IR}\left( \underset{.}{\lambda} \right)} = {{I\; 0\left( \underset{.}{\lambda} \right)*10} - {2\left( {{F\; 1(\lambda)m\; 1} + {F\; 2(\lambda)m\; 2} + {{{Fp}(\lambda)}{mp}}} \right)*{\quad{\left\lbrack {{R\; 1(\lambda)} + {10^{{- 2}{({{F\; 3{(\lambda)}m\; 3} + {F\; 4{(\lambda)}m\; 4} + {f\; 5{(\lambda)}}})}m\; 5}*R\; 2\left( \underset{.}{\lambda} \right)*\left( {1 - {R\; 1\left( \underset{.}{\lambda} \right)}} \right)2}} \right\rbrack*{C(\Omega)}}}}}} & (6) \end{matrix}$

When the ophthalmic system 100 of FIG. 1 is capable of providing a significant number of wavelengths, within the visible region of the spectrum between approximately 380 nm and 720 nm, then a sufficient number of measurements are provided allowing a solution to the unknown m_(i) values to be obtained from the multiple simultaneous equations (6). Further, from these multiple measurements estimates of the F_(i)(λ) and Ri(λ) spectral absorption, and the spectral reflection functions for each optical layer in the eye may be determined. It would be evident to one skilled in the art that using determination of oxygen saturation in retinal vessel proves to be very difficult when a limited numbers of measured wavelengths are used. However, with rapid tunable filters and fast CCDs obtaining such measurements is fast.

Further, having digital data allows the process to correct for issues such as movement of the patients retina, variations in optical source intensity etc. It would therefore be apparent to one skilled in the art that the approach provides for fast, accurate and reproducible evaluation and analysis of ocular data. Further, having time dependent wavelength data within a relatively short time period provides for correction of other factors.

Additionally, it would be apparent that upon a subsequent examination of the patient the extracted data provides for historical clinical records, which are typically not available for patient's retina, unless they have unusually had images taken due to their exposure to laser sources etc. Anomalies in wavelength dependency are optionally highlighted rapidly prior to detailed analysis, images may be optionally presented to an ophthalmic specialist as color coded variances from a previous evaluation, or a new algorithm may be employed to analyze previously stored records.

Hence, if we consider that a new technique for measuring hemoglobin is established with six wavelengths, being 535, 560, 577, 622, 636, and 670 nm, and that these are within the datasets stored for a patient then upon adding a new analysis algorithm to the ophthalmic system 100 the patients hemoglobin data may be historically extracted. It would be evident this is advantageous in expanding clinical records on patients with evolving knowledge in the medical field, and allows subsequent analysis of clinical records to establish previously undetected conditions or determine timing of an onset of a condition or disease.

Referring to FIG. 3 an exemplary flow diagram for an exemplary ophthalmic system 100 is shown providing an hemoximeter functionality to determine the concentration of hemoglobin (Hb), oxygenated Hb, carbon monoxide bound Hb, metallic bound Hb, and sulfurated Hb for the patient's blood using ocular image data.

As shown the process starts at step 301 with the loading of an algorithm to control the ophthalmic system. At step 302 the number of wavelengths to be measured is established from the algorithm, and at step 303 a counter M is set to 1 for the initial measurement. At step 304 a wavelength filter is set to the first wavelength, which may be a wavelength target extracted from a database in reference to the algorithm and the counter M. At step 305 the ophthalmic system captures the image of the patients retina and in step 306 stores the extracted image.

At step 307 the algorithm establishes whether it has completed the imaging process or not. If there are additional wavelengths to be captured then the ophthalmic system returns via step 308 to step 304 in cyclic manner until the sequence is completed. At this point ophthalmic system algorithm resets the counter M to 1. Now the algorithm proceeds to a second analysis sequence starting at step 311 where the first wavelength image is extracted and a physical element within the image identified.

At step 312 the algorithm aligns the extracted image to a predetermined image frame using the physical element identified. Then at step 313 key quantitative data is extracted from the image. At step 314 the algorithm establishes whether it has completed the analysis process or not. If there are additional wavelengths to be captured then the ophthalmic system returns via step 309 to step 311 in cyclic manner until the sequence is completed. In this exemplary algorithm the physical element alignment of each wavelength image allows the movement of the patients eyeball to be removed from the images.

At step 315 a software calculation of the blood factor of interest is undertaken using the extracted quantitative data at steps 313 from the wavelength images. Next the algorithm at 316 adapts a merged image file, determined in this example by additive addition of all image files, for the blood factor. At step 317 the resulting data is formatted and presented to the patient, operator, or ophthalmic specialist as defined by the algorithm before ending at step 318. Such presentation of resulting data may be tabulated data, image data, manipulated image data etc. An option within step 316 is to adjust the images according to the result of an analysis such that a presented image highlights a detected abnormality in results as well as the tabulated data.

It would be apparent to one skilled in the art that such digitally extracted image data can be stored not only centrally within an ophthalmic centers databases but may also be stored within a smart card embedded within a patients health card. Such data may be beneficially extracted and analyzed for oxygen saturation in retinal arteries and retinal veins for example during a surgery in trauma and emergency environments to enhance the trauma teams knowledge of the patients normal oxygen saturation and whether ocular measurements in trauma environments are abnormal or not. It would be further apparent that a low cost, portable variant of the ophthalmic system 100 is possible allowing its use in remote environments, within trauma rooms, within wards, etc as well as the more conventional environments for performing routine analysis and assessment of patients.

Beneficially, the method and system presented allow for multiple ophthalmic tests and measurements to be performed from a single instrument, in a single location, without requiring the insertion/removal of multiple test elements and equipment, whilst allowing improved patient ergonomics as the system can compensate for limited eye or head movements during the tests. Further, use of relatively fast and low cost elements provides a multiple test system that optionally performs these measurements in less time than a traditional single examination test of the prior art approaches.

Numerous other embodiments may be envisaged without departing from the spirit or scope of the invention. 

1. A system comprising; an optical source, the optical source comprising at least a control port, the optical source for providing a source optical signal at least one of a plurality of predetermined wavelengths, the one of the plurality of predetermined wavelengths being established in dependence of a control wavelength signal provided to the control port; a detector, the detector comprising at least an output port, the detector for receiving a detected optical signal, generating at least a digital representation of a detected optical signal, and providing the digital representation of a detected optical signal at the output port as a detected electrical signal; an optical coupling, the optical coupling for coupling the source optical signal to a patients eyeball, receiving at least a signal returned from the eyeball of the patient, and providing the reflected optical signal to the detector, the reflected optical signal therefore forming at least a portion of the detected optical signal; and, a controller, the controller being electrically connected to at least the control port and output port, the controller for providing at least one of a plurality of control wavelength signals, receiving the detected electrical signal, and providing a processed electrical signal, the processed electrical signal being determined at least in dependence upon the detected electrical signal, the control wavelength signal, and a predetermined factor.
 2. A system according to claim 1 wherein, the controller provides at least two processed electrical signals during a single sitting of the patient, the two processed electrical signals being provided in response to the controller providing two different control wavelength signals of the plurality of control wavelength signals.
 3. A system according to claim 1 wherein, the controller provides a plurality of processed electrical signals, each of the plurality of processed signals being at least one of dependent upon a different characteristic of the patients eyeball and obtained without a reconfiguration of the system other than providing at least a subset of the plurality of optical wavelengths.
 4. A system according to claim 3 wherein, receiving a signal returned from the eyeball comprises receiving an optical signal that is generated by at least one of scatter signal, specular reflection, fluorescence, raman scattering, speckle signal, and absorption in response to the provided a source optical signal.
 5. A system according to claim 1 wherein, the optical source comprises at least one of a tunable laser, an incandescent bulb, a tunable optical filter, at least one of plurality of predetermined optical filters, a spectrometer, and a multiple solid state light emitting diode.
 6. A system according to claim 1 wherein, the detector comprises at least one of a photodetector and analog-to-digital converter, an array of photodiodes and at least an analog-to-digital converter, and a charge coupled device.
 7. A system according to claim 1 wherein, the optical coupling comprises at least one of a lens, a mirror a beam-splitter, a wavelength filter, a rest and a restraint.
 8. A system according to claim 7 wherein, at least one of the rest and restraint provide a predetermined optical configuration of at least the optical source detector, and patients eyeball.
 9. A system according to claim 1 wherein, the optical coupling provides a predetermined optical configuration of at least the optical source, detector, and patients eyeball.
 10. A system according to claim 1 further comprising; a memory, the memory for storing at least the processed electrical signal.
 11. A system according to claim 10 wherein, the memory comprises a computer memory, a computer disk drive, a computer readable storage medium, a memory drive, a memory chip, a smart card, and a networked computer disk drive.
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. A method comprising; providing an ophthalmic instrument, the ophthalmic instrument comprising at least a multi-wavelength optical source, an optical wavelength filter, and a detector, the ophthalmic instrument for providing a digital output determined in dependence upon at least a state of the machine and the wavelength of the multi-wavelength optical source; providing a rest, the rest for providing a predetermined relationship between a patients head engaged with at least the rest and the ophthalmic instrument; and, determining with a single placement of the patients head with respect to the ophthalmic instrument at least one measurement of a plurality of measurements of the patient, each of the plurality of measurements determined in dependence upon at least the digital output.
 17. A method according to claim 16 further comprising; determining at least a second measurement of the plurality of measurements of the patient, the second measurement being taken during the same sitting of the patient.
 18. A method according to claim 16 wherein, determining with a single placement comprises providing no reconfiguration of the ophthalmic instrument other than a change in the at least one of the multi-wavelength optical source and the optical wavelength filter.
 19. A method according to claim 18 wherein, providing no reconfiguration is other than providing an optical signal to the patients head at one optical wavelength of a plurality of optical wavelengths other than the current optical wavelength of the plurality of optical wavelengths.
 20. A method according to claim 16 further comprising; determining at least a characteristic of a plurality of characteristics of the patient, in dependence upon at least one of a predetermined portion of the plurality of measurements of the patient and a state of the ophthalmic instrument, the predetermined portion of the plurality of measurements at least one of employed as is, employed with a crop applied to reduce a dimension of each measurement, and employed with an offset applied to align all measurements of the plurality of measurements to a common feature.
 21. A method according to claim 20 wherein, the plurality of measurements generated in dependence upon an optical signal from the multi-wavelength optical source relate to at least one of providing the optical signal with a predetermined wavelength sequence of a plurality of wavelengths, at a first predetermined wavelength and multiple predetermined time intervals, and at a second predetermined wavelength act as a probe followed by multiple measurements at least one of predetermined time intervals and predetermined wavelengths after the probe signal has been applied.
 22. A method according to claim 20 wherein, determining a characteristic of the patient further comprises at least one of applying a predetermined process to the plurality of measurements of the patient, employing at least one measurement of the patient from a previous testing of the patient and weighting the determination in respect of a characteristic of the patient.
 23. A method according to claim 20 wherein, determining a characteristic of the patient at least in dependence upon the state of the ophthalmic instrument comprises determining the characteristic in dependence upon at least one of a mathematical algorithm and a computer process, the at least one of mathematical algorithm and computer process being different for each state of the ophthalmic instrument.
 24. A method according to claim 16 farther comprising; storing the at least one characteristic of a plurality of characteristics of the patient.
 25. A method according to claim 21 wherein, storing the at least one characteristic comprises storing at least one of the output of the detector for a predetermined subset of the plurality of wavelengths and the result of a process applied to the output of the detector.
 26. A method according to claim 24 wherein, storing the characteristic comprises storing the characteristic in at least one of a computer memory, a computer disk drive, a computer readable storage medium, a memory drive, a memory chip, a smart card, and a networked computer disk drive.
 27. A method according to claim 24 further comprising; providing the at least one characteristic of a plurality of characteristics of the patient to at least an operator of the ophthalmic instrument.
 28. A method according to claim 24 wherein, providing to at least an operator comprises providing at least one of a visual representation, a text representation, a numerical representation, and a graphical representation of the characteristic to the operator.
 29. A method according to claim 24 wherein, providing the at least one representation further comprises providing at least an indication of an anomaly within the at least one of the characteristic and the plurality of characteristics. 